1. Field of the Invention
This invention relates to radial tire building and, more particularly, to an improved method of splicing one end of the radial ply fabric layer to the other end to form an annular layer of ply stock.
2. Description of the Prior Art
In the construction of radial ply tires, a carcass consisting of one or more plies of elastomericized fabric is built upon a generally cylindrical drum by applying layers of fabric with cords running perpendicular to or in a near perpendicular direction to the edge of the fabric layer. The ply fabric is applied so that the cords run from bead to bead in a direction which is generally parallel to the axis of the drum. Thereafter, the layers of fabric plies are secured by turning the side edges of the plies around a coil of bead wire enclosed in suitable reinforcing and packing strips. The carcass is then shaped to the required toroidal form, after which breaker and tread portions are applied to the crown portion of the carcass. Then, the tire is placed in a suitable mold and is cured.
As each layer of ply stock is wrapped around the carcass, a splice is formed between the ends of the layers in order for the ply layer to achieve an annular shape. This splice is formed in a direction generally parallel to the direction of the cords in the fabric, i.e., in the direction generally parallel to the axis of the drum. To keep the ply splice from opening up or slipping open during assembly, one end of the ply fabric typically overlaps the other end a short distance. This overlapping, or lap splicing, is the traditional and accepted method of placing fabric plies on a tire carcass. The overlap is usually confined to a short distance, and usually only involves a few ply cords. The distance of a typical overlap may be approximately 0.07 to 0.5 inch.
The resulting overlapping splice results in an area of the tire in which the ply reinforcement is increased. Since the double layer of cords in the overlapping splice area exhibit a different tension from the remaining single layer of the carcass cords, there is less cord elongation in the sidewall in the area of the splice. This results in sidewall indentations in the inflated tire.
In an effort to eliminate these indentations, a reinforced butt splice has been developed. This splice involves having the ends of the ply layer abut each other so that no overlapping occurs, and reinforcing the splice with a strip of another material. The reinforcing strip may be, for example, a gum strip made of nylon or a woven material. A major disadvantage of this reinforced butt splice is that it introduces an additional material into the tire, and the interaction of this material with the existing tire material may produce detrimental results. In addition, the reinforcement adds to the weight of the tire and increases material costs.